Gas-filled surge protector with external short-circuiting device

ABSTRACT

A resilient bracket, in the form of an open ring that is placed on the insulator between the two electrodes and whose one end, having two side bars shaped at the sides, forms the short-circuiting link, serves as a device for the external short-circuiting of two electrodes of a gas-filled surge arrester. A spacer, which is made of a material that can be melted and which is inserted between the short-circuiting link and the insulator, holds the side bars at a radial distance from the electrodes. A surge arrester of this sort is suited in particular for arrangement in cartridges for the acceptance of a multiplicity of arresters.

FIELD OF THE INVENTION

The present invention relates to electrical components, and is to beapplied in the structural design of a gas-filled surge arrester that isprovided with an external short-circuit device.

BACKGROUND INFORMATION

Short-circuit device provided with external short-circuit devices arecommon both in two-electrode and in three-electrode surge arresters.They function to protect the surge arrester in long-term loadsituations. Generally, such a short-circuit device contains a structuralelement that can melt at higher temperatures, with the aid of which thetwo electrodes, or the center electrode and one or both end electrodes,are short-circuited.

In a conventional two-electrode arrester of this type, a spring contactand an arrester contact are arranged electrically parallel to the twoelectrodes, the spring contact being held at a distance from thearrester contact by a spacer that is adjacent to the insulator of thearrester and that softens at increased temperatures. This spacer is madeof a glass-fiber-reinforced plastic that is dimensionally stable atnormal operating temperature and that softens at increased temperatures,e.g. polycarbonate. Such a two-electrode arrester is described inEuropean Patent 0 548 587.

In addition, a conventional external short-circuit device for two- andthree-electrode surge arresters is described in WO 87/06399. Thisshort-circuit device is composed of a two-layer clamp made of athermostatic bimetal, the two layers of the clamp passing, over at theirfree ends, into a monostable snap element. In the event of an overload,one part of the snap element functions to bridge the two externalelectrodes of the arrester. In two-electrode arresters, the bimetalclamp sits on the insulator of the arrester.

In U.S. Pat. No. 4,984,125, a conventional three-electrode arrester, anexternal short-circuit device is described that is composed of abracket, made of an open ring, that is placed on the center electrode,the one end of the ring forming, together with arms shaped at the sides,a short-circuiting link. The free ends of the two arms are held at aradial distance from the end electrodes of the arrester by means of aspacer that is made of a meltable insulating material and that isarranged between the center electrode and the short-circuiting link. Thefree ends of the two arms can thereby be provided with special contacts.Instead of using a spacer between the center electrode and theshort-circuiting link, the mentioned contacts can also be coated with aninsulating coating. French Patent No. 2 670 624 describes a similarlyconfigured external short-circuit device that can be used both forthree-electrode and for two-electrode arresters. In this device, thefree ends of the two arms of the short-circuiting link are bent in sucha way that they abut the circumferential edge of the respectiveelectrode, the free ends having in the area of the point of contact aninsulating coating that can melt when heat is applied.

SUMMARY

The object of the present invention is to configure the short-circuitdevice in such a way that it extends radially past the surge arrester aslittle as possible, ensures a safe contacting, and is easy to install.

In order to achieve this object, it is provided according to the presentinvention that the spacer is arranged between the center part of theshort-circuiting link and the insulator.

Such a configuration of the short-circuit device makes use of theconventional design of a short-circuit device such as that described inU.S. Pat. No. 4,984,125, but the bracket, in this context, is placed noton an electrode, but rather—in a manner such as described in FrenchPatent No. 2 670 624)—on the insulator located between two electrodes.In this way, the short-circuiting link is arranged without potential.Given cramped installation conditions (magazine or cartridge), this canprove to be advantageous insofar as no disturbing short circuit canoccur in case of contact of one side of the short-circuiting link with acontact terminal that conducts potential. Since the spacer is arrangedbetween the short-circuiting link and the insulator, the spacer can beof relatively thin construction; in addition, a relatively inexpensivethermoplastic plastic material can be used for the spacer, since theinsulator heats up with a delay relative to the electrodes that are tobe short-circuited.

A surge arrester having short-circuit device configured according to thepresent invention is thus distinguished by a design that is very compactand that saves a great deal of space with regard to the insertion of alarger number of such arresters into cartridges, the short-circuitdevice being able to be made of one or two parts and to be easilyadapted to various arrester geometries due to its simple configuration.The short-circuit device can also be retrofitted; it can also beexchanged after being blown, as long as the actual arrester is stillintact.

The short-circuit device configured according to the present inventioncan be used both for two-electrode and for three-electrode arresters. Inthree-electrode arresters, each of the two insulators present in sucharresters is to be equipped with a short-circuit device of the presentconfiguration.

The open snap-on ring of the new short-circuit device can be made of aheat-resistant plastic or of a resilient (spring-like) metal thatconducts less well electrically (e.g. spring steel or a copper alloy), ametallic short-circuiting link that conducts very well electrically(e.g. made of copper) being placed onto the one end of the open ring orbeing fastened there in some other way. Preferably, however, the openring is made of the same material as the actual short-circuiting link,and is configured in one piece with the latter, the open ring beingprovided at the one end with two side bars, shaped at the sides, for theformation of the short-circuiting link. In order to improve thecontacting, these side bars can be bent slightly at their free ends.

A plastic part that can be melted may be used as a spacer for theshort-circuit device. In the same way, a spacer made of a solderingmaterial can also be used. These spacers can, for example, have the formof a rivet fastened to the center part of the link. Alternatively, aplastic clip placed on the center part of the link can also be used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a gas-filled surge arrester having two electrodes, equippedwith a short-circuit device according to the present invention.

FIG. 2 shows the short-circuit device without arrester.

FIG. 3 shows a surge arrester in which the spacer of the short-circuitdevice is a rivet.

FIG. 4 shows a surge arrester having a short-circuit device in which thespacer is a plastic clip.

FIG. 5 shows a short-circuit device having a special configuration ofthe electrodes of the arrester.

FIG. 6 shows a three-electrode arrester having two short-circuit devicesplaced on the two insulators.

DETAILED DESCRIPTION

FIG. 1 shows a surge arrester 1 including an insulator 2 and two endelectrodes 3 and 4. A short-circuit device 10 is placed on insulator 2,the device including an open ring 11 (shown separately in FIG. 2) madeof cold-hammered metal and an insulating spacer 20. Open ring 11 isfashioned, in this context, as a short-circuiting link 12 at its oneend, and has a center part that runs in planar fashion and two side bars14 and 15 that are shaped at the sides and that are bent slightly at theends. The axial length of short-circuiting link 12 is thus chosen suchthat the short-circuiting link does not extend past the surge arresteraxially (see also FIG. 5). Spacer 20 can also be made of a solderingmaterial.

According to FIG. 3, the short-circuit device for arrester 1 is likewisecomposed of an open ring that can be snapped onto the insulator of thearrester, a plastic rivet 21 being provided as a spacer for actualshort-circuiting link 13, the rivet being fixed in a bored hole ofcenter part 13 of the short-circuiting link. According to FIG. 4, aplastic clip 22 that is pushed onto center part 13 of theshort-circuiting link can be used as a spacer.

According to FIG. 5, electrodes 31 and 32 of the surge arrester areprovided with a larger outer diameter than insulator 2. The bending ofthe ends of actual short-circuit device 16 at the ends thus becomesunnecessary.

FIG. 6 shows an arrester in which another center electrode 5 is arrangedbetween end electrodes 3 and 4, the arrester being composed of twoinsulators 6 and 7. A short-circuit device 10, as is also used for thearrester according to FIG. 1, is placed onto each insulator.

What is claimed is:
 1. A gas-filled surge arrester, comprising: at leasttwo electrodes; an insulator arranged between the electrodes; and anoverload fuse, the overload fuse including an external short-circuitdevice, the short-circuit device including a first short-circuitinglink, a holding device and a spacer, the first short-circuiting linkbeing electrically conductive and extending in an axial direction of thesurge arrester, ends of the short-circuiting link being held at a radialdistance from the electrodes by the holding device, the holding deviceexerting a spring force via the spacer, the spacer melting when heat isapplied, the holding device including an open ring that can be snappedonto the insulator and being made of a strip-shaped resilient material,the first short-circuiting link being arranged on one end of the holdingdevice, the spacer being arranged between a center portion of the firstshort-circuiting link and the insulator and being out of contact withall electrodes.
 2. A gas-filled surge arrester, comprising: at least twoelectrodes; an insulator arranged between the electrodes; and anoverload fuse, the overload fuse including an external short-circuitdevice, the short-circuit device including a first short-circuitinglink, a holding device and a spacer, the first short-circuiting linkbeing electrically conductive and extending in an axial direction of thesurge arrester, ends of the short-circuiting link being held at a radialdistance from the electrodes by the holding device, the holding deviceexerting a spring force via the spacer, the spacer melting when heat isapplied, the holding device including an open ring that can be snappedonto the insulator and being made of a strip-shaped resilient material,the first short-circuiting link being arranged on one end of the holdingdevice, the spacer being arranged between a center portion of the firstshort-circuiting link and the insulator; wherein the at least twoelectrodes includes three electrodes, and further comprising: a secondinsulator; and a second external short-circuit device including a secondshort-circuiting link placed on the second insulator.
 3. Thesurge-arrestor according to claim 2, further comprising a second spacerarranged between the second short-circuiting link and the secondinsulator, the second spacer melting when heat is applied.
 4. Agas-filled surge arrester, comprising: at least two electrodes; aninsulator arranged between the electrodes; and an overload fuse, theoverload fuse including an external short-circuit device, theshort-circuit device including a first short-circuiting link, a holdingdevice and a spacer, the first short-circuiting link being electricallyconductive and extending in an axial direction of the surge arrester,ends of the short-circuiting link being held at a radial distance fromthe electrodes by the holding device, the holding device exerting aspring force via the spacer, the spacer melting when heat is applied,the holding device including an open ring that can be snapped onto theinsulator and being made of a strip-shaped resilient material, the firstshort-circuiting link being arranged on one end of the holding device,the spacer being arranged between a center portion of the firstshort-circuiting link and the insulator; wherein the spacer is made of arivet that is fastened to the center portion of the firstshort-circuiting link, the rivet being formed of one of a plasticmaterial and a soldering material.